Device for the removal of smoke from electric furnaces and the like



March 31, 1964 E RNl ETAL 3,127,462

E DEVICE FOR THE REMOVAL OF SMOKE FROM ELECTRIC FURNACES AND THE LIKEFiled Feb. 13. 1961 A 18 1/ J L17 f Fig.2

1NV5NToRs= E uuco RN/ no ATTORNEY United States Patent 3,127,462 DEVICEFGR THE REMOVAL OF SMOKE FRUM ELECTRIC FURNACES AND THE LIKE Enrico Erniand Fritz Liischer, Gerlafingen, Switzerland,

assignors to Gesellschaft der Ludw. von Rollschen Eisenwerke A.G.,Gerlafingen, Switzerland, a corporation of Switzerland Filed Feb. 13,1961, Ser. No. 88,982 Claims priority, application Switzerland Feb. 17,1960 13 Claims. (Cl. 13-3) The present invention relates to an improveddevice for the removal of smoke from electric furnaces, and morespecifically, to a novel design and construction of a smoke hood readilysuitable for exhausting smoke and combustion gases from a furnaceinterior.

Electric furnaces, particularly those presently widely employed formetallurgical purposes, are provided with at least one electrode and anelectric arc is formed between the electrode and the stock to be melted.In the melting processes carried out in such a manner, large quantitiesof smoke gas are generally generated which may partly originate from themelting stock and partly from the burnt-off electrode. The effectiveremoval of these produced gases constitutes a major problem forindustry. It is necessary that these gases be removed as completely aspossible, not only to protect the operators against the toxic componentsof the gases (CO from the consumption of carbon electrodes), but alsobecause of the considerable dust content generally present in the gasand, the necessity imposed thereby of cleaning the gases from dust priorto their escape into the atmosphere. Various proposals have been made inorder to solve this problem with open-hearth electric furnaces byproviding a movable smoke hood. In closed electric furnaces, openingsfor the removal of smoke gases have been proposed in the coverof thefurnace; such openings, however, are arranged independently of andseparate from the electrode opening. This separate arrangement of thegas escape openings has various operational disadvantages; of particularimportance is the virtual impossibility of entirely preventing smokefrom issuing along the electrodes. While it would, as such, be possibleto prevent the smoke gas from escaping in the region of the electrodesby adequately raising the suction operating on the furnace interior,such may cause air to enter into the furnace. This is a disadvantage forseveral reasons, one of which is the danger of burning the electrode atits shaft. It has also been found that the flow conditions in the knownexhausting devices for the smoke gas are not always very favorable.

The device according to the present invention is designed to eliminatethe disadvantages encountered when employing the heretofore known smokeremoval installations, and more particularly, those used with closedelectric furnaces. The smoke removal device according to the presentinvention is provided with an annular housing which substantiallycoaxially encloses an electrode at the point where'it emerges from thefurnace and, further, is provided witha suction slot which communicateswith an exhaust duct in the interior of the housing.

The device according to the present invention enables the smoke to becollected immediately above the region where its development is mostpronounced. It is to be appreciated that the generation of smoke andgases is most pronounced at the point where the electrode enters thecharge. However, as a practical matter the smoke cannot be effectivelyremoved immediately at this point. The gases and air which collect aboutthe surface of the electrode are caused to rise in temperature and forman upwardly directed current which finally collects underneath thefurnace cover at the point where the electrode piercingly enters thiscover member. It is at this locality that the device of the presentinvention operates to remove smoke therefrom. Thus, the normal upwarddraft of the smoke gases and the like situated about the electrode is afactor directly contributing to the effective removal of smoke and thelike. It is to be understood that a separate device for the removal ofsmoke and combustion gases or the like is preferably associated witheach electrode of the furnace in practical operation.

Accordingly, it is an important object of the present invention toprovide means for effectively removing smoke and the like from theinterior of electric furnaces.

Another important object of the present invention is to provide meansfor removal of smoke from electric furnaces in such a manner as toprevent depositing of solid or foreign particles in the flow channelsprovided for the removal of such smoke.

Still a further object of the present invention is to provide means foreffectively removing smoke gases from a furnace interior with thevelocity of flow of the gases to be removed being maintained as uniformas possible.

These and still further objects and the entire scope of applicability ofthe present invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

In the drawings:

FIGURE 1 is a cross-sectional, fragmentary view of a smoke removaldevice carried by the upper portion of a closed electric furnace in theregion where the electrode enters the furnace interior; and

FIGURE 2 is a cross-sectional view of the smoke removal device shown inFIGURE 1, taken along line AA thereof.

It is to be understood that only enough of the structure of the presentdevice has been shown which will enable one to have a clearunderstanding of the teachings of the present invention. The details ofthe electrode and the furnace have been omitted for the sake of clarityin explanation.

Referring now to the drawing and, more particularly to FIGURE 1, thereis shown a cover member 1 provided for an electric furnace and having anannular or circular opening 2 arranged to receive an electrode adaptedto be inserted through said annular opening. The smoke removal device 3comprises an annular housing 4 communicating with an exhaust conduit 5.A flange member 6 connects the conduit 5 with an exhaust system for thefurnace, generally designated by reference numeral 7. The annularhousing 4 may be arranged in the annular opening 2 of the electricfurnace and, generally, comprises a lower base portion 8, an upperhousing portion 9 and an intermediate connecting wall portion 17. Thelower base portion 8 of the housing 4 includes an arcuate wall portion8a having a downwardly, annular extending wall 8b which extends into theannular opening 2 and is adapted to bear against the inner wall 2athereof to partly protect this annularopening 2. The upper housingportion 9 consists of an upper annular wall Qa and a downwardlyextending wall portion 9b. The wall portion 9a inclines upwardly in thedirection of the conduit 5, whereas the downwardly extending wallportion 9b continually widens in the direction of the conduit 5. Thelower edge of the wall portion 9b is spaced a predetermined distancefrom the inner wall of the base portion 8 to define an annular slot 10through which the smoke gases or the like, collecting in the space 11 atthe point where the electrode passes through the cover 1, may be passedinto an annular flow channel 18 formed between the upper and 'lower wallportions 9 and 8 respectively. The flow chansmoke gases removed shouldbe maintained as uniform as possible and of sufficient magnitude toensure that the solid particles are carried along in the flow stream anddo not deposit themselves in the flow channel. The minimum velocity offlow necessary to obtain the so-called dragging effect of the solidparticles is determined by a number :of factors; particularly by thetype, size and distribution .of the solid material being handled, as forexample dust. It has been found that in electric furnaces used for theprocessing of iron and for removing the dust or fine particles resultingtherefrom, a minimum velocity of flow of the'gasshould amount toapproximately meters/sec. Additionally, suitable means such asvibrators, may be employed to prevent solid particles from beingdeposited on the walls of the smoke removal housing, which housing maybe formed of individual segments.

In order to achieve a uniform velocity of the gases or smoke to beexhausted, the cross-sectional area of the flow channel 18 must bedimensioned such that it increases radially in linear relationship inthe direction of flow. That is to say, radial planes taken through theflow channel 18 at various spatial points through this flow channelclearly show an increase of the cross-section area of the flowchannel inthe direction of the exhaust conduit 5. Such an increase ofcross-sectional area of the flow channel is effectively obtained in theembodiment of FIG- URE 1 since the wall portion b of the upper wall 9 isdesigned'to widen in an upward direction and exhibits a helicalconfiguration, in the form of a half-turn of a screw, from the pointwhere the cross-sectional area of the flow channel is smallest to thatwhere it is largest. It is to be appreciated that the width of theannular intake slot 10 between the upper housing portion 9 and the lowerhousing portion 8 should be suitably dimensioned in order to accommodatethe volume of smoke gas handled; into account must be taken the gassuction output available for the smoke or gas handled.

During the operation of the furnace, a field of force 'is formed aboutthe electrode which produces induced currents in a metallic and magneticmaterial which may cause operational trouble. The materials handled bythe furnace and which generate the smoke to be removed, includenon-magnetic materials such as ceramic materials or non-magnetic metalssuch as brass, and magnetic materials such as iron because of itsfavourable thermal stability and relatively low cost. If magneticmaterials are used an intermediate layer formed of a non-magneticmaterial may be provided according to one embodiment of the invention.Such a layer is provided to counteract the formation of inducedcurrents. For this purpose a layer formed of non-magnetic material isincorporated between the wall portions of the housing segments,preferably at the narrowest point of the cross-section of the flowchannel 18 provided in the annular housing 4. The layer at leastpartially separates the two halves of the housing 4, that is to say, therespective portions located in front of and behind the plane of thedrawing of FIGURE 1. This non-magnetic layer may also be in the form ofa sheet arranged so as to divide the flow channel 18 into two halves.Such an arrangement may be of considerable advantage with respect to theconditions of flow provided that this partition is accurately located atthe point where the velocity of flow is smallest. In FIGURE 2 we haveshown such a partition member 20 which is formed of a non-magneticmaterial. If the smoke removal device is formed of a material which isnot readily capable of withstanding the thermal stresses due to the heatfrom the furnace and the electrode, a cooling system may be providedtherewith. In the embodiment according to FIG- URE 1, the housing 4may-be provided with a cooling compartment 1h formed between the innerand outer walls of the housing in the form of a cooling jacket. Acooling medium such as water may be passed through the compartment 19formed between these two walls.

In FIGURE 2 there is shown a cross-sectional view taken along line A-Aof FIGURE 1. An outer furnace wall 12 supports the smoke removal device3. An electrode member, schematically illustrated in cross-section bythe phantom lines 15, passes through the central aperture 14 of thesmoke removal device 3 into the furnace interior. The outer periphery ofthe electrode 15 is spaced from the edge 9c of the upper housing portion9 and defines an airgap 16 between the electrode and'the annular upperportion 9 of the housing 4. This airgap 16 may be sealed by means of aloosely arranged sealing ring if provision can be made that no shortcircuit will occur between the electrode and ground. However, since theprovision of an effective seal between the electrode and the furnaceconstitutes a problem which has not been satisfactorily resolved up tothe present, a preferred embodiment of the invention provides a solutionfor such a sealing problem. This is done by arranging a control memberbetween the electrode 15 and the housing 4 of the smoke removal device.This control member may be, for example, a pressure probe which respondsto the conditions of gas flow. As a result, it is possible toautomatically control the gas removal output in such a manner that theflow velocity of the fluid medium appearing in the airgap 16 between theelectrode 15 and the housing 4 practically amounts to zero. A zero valueof flow velocity at this point indicates that gas cannot emerge from thefurnace nor air enter into it. Since practical operation of the furnacemay possibly render it difiicult when employing several electrodes, suchas three or six electrodes, to avoid varying flow conditions in theindividual gas exhaust ducts, each smoke removal device provided for theindividual electrodes is preferably connected'to its own dust removaldevice and suction unit (exhaust system). The suction effect of eachexhausting or suction unit may be controlled by the pressure probeprovided for each respective suction unit. Such an arrangement isdesigned to ensure that the entry of air and the escape of gases at theelectrodes is effectively inhibited even if several electrodes areemployed.

Having thus described the present invention, what is desired to besecured by United States Letters Patent, is:

'1. A device for removal of smoke gas and the like from the interior ofa furnace adapted to encircle an electrode at the region where saidelectrode enters said furnace, said device comprising an annular housingprovided with an outlet conduit for removal of said gas and an internalannularly arranged flow'channel communicating with said outlet conduit,with the cross-sectional area of said annularly arranged flow channelincreasing in the direction of said outlet conduit, said housing being.provided with annular slot means in registry with said flow channelpermitting movement of smoke gas into said flow channel.

2. A device according to claim 1, wherein partition means are arrangedatthe region of smallest cross-sectional area of said flow channel-todivide said flow channel into two substantially symmetrical segments.

3. A device according to claim 1, wherein said annular housing isconstructed to provide an annular airgap adapted to receive a controlmember responsive to the gas flow.

4. A device according to claim 1, wherein at least a portion of saidannular housing includes means formed of a non-magnetic material forcounteracting the formation of induced currents.

5. A device according to claim 4, wherein said means formed ofnon-magnetic material is located at the point of narrowest cross-sectionof said flow channel for counteracting the formation of inducedcurrents.

6. A device according to claim 1, wherein said annular housing isprovided with means permitting circulation of a cooling medium throughsaid annular housing for cooling thereof.

7. A device according to claim 7, wherein said cooling means is acooling compartment adapted to receive a cooling medium.

8. A device according to claim 1, wherein said annular housing includesa downwardly extending portion.

9. A device according to claim 1, wherein said outlet conduit isintegral with said annular housing.

10. A device for removal of smoke gas and the like from the interior ofa furnace adapted to encircle an electrode at the region where saidelectrode enters said furnace, said device comprising an imperforateannular housing provided with an outlet conduit for removal of said gas,said annular housing having an upper housing portion, a lower baseportion and an intermediate wall portion interconnecting said upperhousing portion with said lower base portion to define an annular flowchannel, said upper housing portion including an upper wall portion anda downwardly extending wall portion terminating at a predetermineddistance from said lower base portion to define an annular slot, saidannular flow channel communicating with said outlet conduit with saidannular slot in registry with said annular flow channel.

11. A device for removal of smoke gas and the like from the interior ofa furnace adapted to encircle an electrode at the region where saidelectrode enters said furnace, said device comprising an annular housingprovided with an outlet conduit for removal of said gas, said annularhousing having an upper housing portion, a lower base portion and anintermediate wall portion interconnecting said upper housing portionwith said lower base portion to define an annular flow channel, saidannular flow channel increasing in cross-sectional area in the directionof said outlet conduit, said upper housing portion including an upperwall portion and a downwardly extending wall portion terminating at apredetermined distance from said lower base portion to define an annularslot, said annular flow channel communicating with said outlet conduitwith said annular slot in registry with said annular flow channel.

12. A device for removal of smoke gas and the like from the interior ofa furnace adapted to encircle an electrode at the region where saidelectrode enters said furnace, said device comprising an annular housingprovided with an outlet conduit for removal of said gas, said annularhousing having an upper housing portion, a lower base portion and anintermediate wall portion interconnecting said upper housing portionwith said lower base portion to define an annular flow channel, saidupper housing portion including an upper wall portion and a downwardlyextending wall portion terminating at a predetermined distance from saidlower base portion to define an annular slot, said upper wall portioninclining upwardly in the direction of said outlet conduit and saiddownwardly extending wall portion increasing in width in the directionof said outlet conduit such that said annular flow channel increases incross-sectional area in the direction of said outlet conduit, saidannular flow channel communicating with said outlet conduit with saidannular slot in registry with said annular flow channel.

13. A device according to claim 12, wherein said widening, downwardlyextending wall portion is helically curved in the manner of at least aportion of a screw line.

References Cited in the file of this patent UNITED STATES PATENTS2,761,003 Richardson Aug. 28, 1956 FOREIGN PATENTS 198,225 SwitzerlandSept. 1, 1938

1. A DEVICE FOR REMOVAL OF SMOKE GAS AND THE LIKE FROM THE INTERIOR OF A FURNACE ADAPTED TO ENCIRCLE AN ELECTRODE AT THE REGION WHERE SAID ELECTRODE ENTERS SAID FURNACE, SAID DEVICE COMPRISING AN ANNULAR HOUSING PROVIDED WITH AN OUTLET CONDUIT FOR REMOVAL OF SAID GAS AND AN INTERNAL ANNULARLY ARRANGED FLOW CHANNEL COMMUNICATING WITH SAID OUTLET CONDUIT, WITH THE CROSS-SECTIONAL AREA OF SAID ANNULARLY ARRANGED FLOW CHANNEL INCREASING IN THE DIRECTION OF SAID OUTLET CONDUIT, SAID HOUSING BEING PROVIDED WITH ANNULAR SLOT MEANS IN REGISTRY WITH SAID FLOW CHANNEL PERMITTING MOVEMENT OF SMOKE GAS INTO SAID FLOW CHANNEL. 